Activation of textile forms of carbon



United States Patent 3,256,206 ACTIVATION 0F TEXTILE FORMS OF CARBON Ernest G. Doying, Rocky River, Ohio, assignor to Union Carbide Corporation, a corporation of New York No Drawing. Filed Dec. 3, 1964, Ser. No. 415,775

8 Claims. (Cl. 252421) This application is a continuation-in-part of application Serial No. 162,929, filed December 28, 1961.

This invention relates to a novel process for the activation of carbon, and more particularly, to the activation of textile forms of carbon which are of a cellulosic origin.

Carbon in a flexible fiber and fabric form has recently become commercially available. Flexible carbon in any textile form such as yarns, braids, felts, or fabrics that are woven or knit has been reported. These textile materals are thermally converted directly from a cellulosic state to a carbonaceous state.

These textile forms of carbon are characterized by the chemical and electrical properties of carbon while generally retaining the characteristic physical textile attributes of the cellulosic starting textile materal, such as -a high tensile strength and flexibility, and the ability to With stand creasing and folding.

Two standard methods for providing activated carbonaceous materials have been known and practiced for many years. One method is referred to as gas activation and consists of oxidizing a partially carbonized material such as charcoal with steam, carbon dioxide, or flue gas at a temperature between about 800 C. and 1000 C. A variation of this method comprises mixing the charcoal with limestone which is then thermally decomposed so as to liberate carbon dioxide which then performs the actual activation of the charcoal. The second method is referred to as chemical activation and comprises impregnating an uncarbonized material such as sawdust with chemicals such as zinc-chloride, phosphoric acid or potassium sulfide, calcining to 500-900 C. to dehydrate and degrade the sawdust to carbon and subsequently removing the remaining chemicals from the residual carbon by acid or water washing.

Unfortunately, it has been discovered by the applicant that these conventional procedures are unsuitable for the activation of the textile forms of carbon. Obviously, shaped fibrous forms of carbon cannot withstand the same amount of rough treatment as lumps of charcoal or sawdust. In addition, uniform activation of the textile form of carbon is virtually impossible by the conventional gas activation methods.

The principal object of the invention is to provide a gas activation process suitable for the uniform activation of textile forms of carbon.

Broadly stated, the object of the invention is accomplished by a process which comprises covering the carbon textile material to be activated with a cover of a fine mesh carbon material Which will burn in air, and rapidly heating the textile material and the carbon cover to a temperature between about 800 C. and 1000 C. in the presence of air in order to oxidize the carbon cover, thereby activating the carbon textile material. When the activation has been completed, the activated material and cover are cooled rapidly to minimize as much as possible the quantity of air which could penetrate the carbon cover and burn the activated material.

The carbon cover performs a dual function in the process of the invention. It serves as a protective barrier to prevent active burning of the carbon textile material and it also uniformly generates the activating gas (presumably CO overthe entire area of the carbon textile material. In this manner, uniform gas activation is obtained.

In the practice of the invention, many different fine mesh carbonized materials are suitable as the carbon 3,256,206 Patented June 14, 1966 "ice cover to be burned. Included among these are wood charcoal, coal, coke (-wood, coal, or petroleum), and Y graphite. Best results are accomplished with particle sizes of from about 6 mesh to about mesh. Larger particles would permit too much diffusion of oxygen and smaller particles would permeate the. carbon textile material.

The depth or thickness of the carbon cover is not critical and forms no part of the inventive concept. It is within the ordinary skill of the artisan to select a depth which is suitable for the proper performance of the carbon cover in accordance with the dual function outlined above. A practical range of depth may be suggested between A and 3 inches.

The degree of activation is controlled by the duration of the activation process, the temperature of the carbon cover and the carbon textile material, and the oxidation rate of the carbon cover. The duration of the activation process is a function of the desired level of activity, the thickness and particle size of the carbon cover, the reactivity of the carbon cover, the oxygen concentration in the furnace, and the thickness and size of the textile material being activated. No particular combination of dimensions or quantities may .be absolutely assigned to these variables; rather, some various possible combinations are best illustrated by the examples which follow.

I EXAMPLE I A five inch circle of carbonized viscose rayon felt, onequarter of an inch thick, and which had been calcined to 700 C. was placed on the bottom of a quartz dish five and one-eighthinche-s in diameter by /8 inch deep. The carbon felt was then completely covered by a layer of packing coke about five-eighths of an inch deep. The dish was placed for one hour in the mufile of an electric furnace which had been heated to a temperature of 970 C., while air was passed through the mufiie at the rate of three liters per minute. The mufile measured seven and onehalf inches by seven and three-quarter inches by fourteen inchesdeep inside. At the end of the heating the dish was withdrawn and rapidly cooled. The rapid cooling process was accomplished by air quenching the dish which was placed on a cold surface. Air was prevented from contacting the coke or felt during the cooling period by placing a cover of sheet asbestos over the dish and securing it in place with a heavy object, such as a brick.

EXAMPLE II Identical to Example I except that the charged dish was left in the heated muffie for two hours.

EXAMPLE III Identical to Example 1 except that the charged dish was left in the heated mufile for three hours.

In each case, the felt sample was weighed before and after treatment, and the weight of the coke cover was .similarly determined before and after the baking step. The treated felt was tested by conventional methods to determine its activity and retentivity with respect to carbon tetrachloride. The data obtained in such tests are set forth in the following table.

It is important to note that each felt sample tested exhibited a uniformly distributed activation character, that is, no one area of any sample was activated to a substantially greater degree than a comparable area of the same sample. This accomplishment represents a substantial improvement over prior art conventional gas activation methods which generally activate those areas nearest the gas source to a greater degree than those furthest away from the source.

Several tests were undertaken in which carbon textile materials similar to those in Examples I-III were activated with CO gas and steam in a conventional manner. The tests employed an apparatus which comprised three hollow boxes coaxially situated one within the other, so structured that each was separated by a suitable space. Activating gas was allowed to enter one end of the outer box. The gas then flowed through the space between the outer box and the middle box to the other end of the boxes where it was permitted to enter the space between the two inner boxes. The gas then flowed through this space and into the inner box. In this manner the gas was preheated and thereby maintained a uniform temperature within the inner chamber.

The following examples illustrate specific tests employing this apparatus.

EXAMPLE IV A rack containing three shelves of wire gauze was provided to support the carbon textile samples within the inner box. Nine pieces of A thick carbon felt seven centimeters wide by eight centimeters long were arranged on the three shelves, each shelf having three of the nine samples. The entire assembly was then placed in a large muffie furnace and nitrogen gas was passed through the apparatus at a flow rate of four liters per minute until a temperature of 822 C. was obtained in the activating chamber. CO gas was introduced at the same flow rate to replace the nitrogen gas. The temperature was maintainedat this constant value for one hour. The apparatus was then withdrawn from the furnace and cooled while nitrogen gas flowed through the system to prevent further oxidation.

EXAMPLE V Identical to Example IV except that six pieces instead of nine pieces of carbon felt were employed. Three pieces were placed on the inlet side of the inner chamber and three pieces were placed at the exit end of the inner chamber.

EXAMPLE VI Identical to Example V except that steam was used in place of C The results obtained from the tests of Example IV may best'be summarized by the following table:

Table 2 clearly shows that those samples which were nearer the entrance were activated to a substantially higher degree than those which were positioned nearer the exit.

In the test of Example V, the three pieces of carbon felt on the inlet gas side of the box were half burned.

These three samples had an average yield of 31.0 percent and an average activity of 78.8 percent. The three samples which were positioned nearer the exit end had an average yield of 81.5 percent and an activity of about 27.5 percent.

The results ofthe test of Example VI were similar to those of Example V. In this case, however, the three samples on the gas inlet side were completely consumed and only 45 percent of the other three pieces were recovered.

The activated textile carbons of the invention, such as activated carbon wool, carbon felt, or carbon cloth have many applications. For example, they may be advantageously employed as gas mask filters, cigarette filters and in the making of adsorbent protective clothing. In addition, filters of carbon wool or felt could be employed for air conditioning purposes in fallout shelters, submarines and manned space craft.

I claim:

1. A process for the uniform activation of a textile carbon article of cellulosic origin which comprises completely covering said carbon article with a cover of fine mesh carbon material which will burn in air, subjecting said article and cover to a temperature between about 800 to 1000 C. in the presence of air thereby uniformly activating said carbon textile article, and rapidly cooling said article and cover to minimize the access of air to said article.

2. The process of claim 1 wherein said fine mesh carbon cover is made up of a material chosen from the group consisting of wood charcoal, coal, wood coke, coal coke, petroleum coke, and graphite.

3. The process of claim 1 wherein said fine mesh carbon cover comprises particle sizes of from about 6 mesh to about mesh.

4. The proces of claim 1 wherein said textile carbon article is carbon felt and said fine mesh carbon cover is petroleum coke.

5. A proces for the uniform activation of a carbonized felt of viscose rayon origin which comprises completely covering said carbon felt with a cover of packing coke, placing said coke covered carbon felt in an open dish, placing the entire assembly in the muflle of an electric furnace which has been heated to a temperature between about 8001000 C., maintaining s'aid assembly in said furnace for at least one hour while simultaneously passing air through said mufile, removing said coke covered carbon felt and said dish from said mufile, and rapidly cooling said assembly under a cover of sheet asbestos to minimize the access of air to said carbon felt.

6. The process of claim 5 wherein said cover of packing coke comprises particles of fine mesh, said particles having sizes of from about 6 mesh to about 100 mesh.

7. The process of claim 6 wherein said furnace is at a temperature of approximately 970 C. and said air is passed through said muffle at a rate of about three liters per minute.

8. The process of claim 7 wherein'said rapid cooling consists of placing said dish on a cold surface and quenching said dish with air.

References Cited by the Examiner UNITED STATES PATENTS 1,249,041 12/1917 Demme 252-421 2,002,651 5/1935 Wickenden 252421 3,053,775 9/1962 Abbott 252-421 BENJAMIN HENKIN, Primary Examiner.

MAURICE A. BRINDISI, Examiner.

H. S. MILLER, Assistant Examiner. 

1. A PROCESS FOR THE UNIFORM ACTIVATION OF A TEXTILE CARBON ARTICLE OF CELLULOSIC ORIGIN WHICH COMPRISES COMPLETELY COVERING SAID CARBON ARTICLE WIH A COVER OF FINE MESH CARBON MATERIAL WHICH WILL BURN IN ARI, SUBJECTING SAID ARTICLE AND COVER TO A TEMPERATURE BETWEEN ABOUT 800 TO 1000*C. IN THE PRESENCE OF AIR THEREBY UNIFORMLY ACTIVATING SAIC CARBON TEXTILE ARTICLE, AND RAPIDLY COOLING SAID ARTICLE AND COVER TO MINIMIZE THE ACCESS OF AIR TO SAID ARTICLE. 